Abstract: 【Objective】The effects of lufenuron on the growth and development of Spodoptera frugiperda（Smith）larvae and the diversity of intestinal bacteria were analyzed，and the response mechanism of Spodoptera frugiperda（Smith） to lufenuron stress was explored，which provided scientific basis for the rational usage of lufenuron to control Spodoptera frugiperda（Smith）and its resistance mechanism.【Method】The toxicity of 10% lufenuron suspension to the 3^rd instar larvae of Spodoptera frugiperda（Smith）was determined by leaf dipping method，and the lethal medium concentration （LC₅₀）on the 3^rd instar larvae of Spodoptera frugiperda（Smith）was determined. Intestinal culturable bacteria of 3^rd instar larvae of Spodoptera frugiperda（Smith）in lufenuron LC₅₀ treatment group and Tween-20 treatment control group were isolated by isolation culture method，and the species of the isolated culturable bacteria were identified according to the colony morphology and 16S rDNA sequence.【Result】Lufenuron showed strong toxicity against the 3^rd instar larvae of Spodoptera frugiperda（Smith），and its toxicity increased with the increase of concentration and treatment time. The LC₅₀ was 1.162 mg/L at 96 h after exposure to agent. Nine strains of culturable bacteria were isolated from the intestine in 3^rd instar larvae of lufenuron LC₅₀ treatment group，belonging to 6 genera in 6 families under 4 phyla，while the control group had 13 strains belonging to 8 genera in 7 families under 4 phyla. At the phylum level，after lufenuron LC₅₀ treatment，the relative abundance of Firmicutes，Proteobacteria and Actinobacteria decreased by 10.15%，6.01% and 0.09% respectively compared to control group，and the relative abundance of Bacillota increased by 16.24%. At the genus level，the relative abundance of Enterococcus，Enterobacter and Staphylococcus decreased by 6.64%，4.65% and 2.14% respectively compared with the control，and the relative abundance of Bacillus increased by 16.24%.【Conclusion】Lufenuron has great effects on the structure，function and diversity of its intestinal flora of Spodoptera frugiperda（Smith）.